means A sudden, involuntary contraction of a muscle, or by extension any brief uncontrollable burst of feeling or activity.

from From Greek 'spasmos,' a cramp or convulsion, from the verb 'span,' meaning to draw, pull, or stretch tight — the same root that ties muscles into knots. It traveled through Latin 'spasmus' and Old French before settling into English in the late medieval period, still carrying that core image of something pulled taut against its will.